Add pipeline execution logs to JSON file

[renezander030]

What

Write a structured JSON log for each pipeline run — inputs, step results, token usage, approval decisions, timestamps.

Why

The audit trail is a core selling point of FixClaw, but currently logs only go to stdout. A JSON log file per run makes it easy to review, search, and archive pipeline history.

Scope

• Create a logs/ directory (gitignored)
• After each pipeline run, write a JSON file: logs/{pipeline-name}-{timestamp}.json
• Include: pipeline name, start/end time, each step's name/type/status/duration, token counts for AI steps, approval decisions and who approved
• Keep it append-friendly (one file per run, not one big file)

Helpful context

• Go's encoding/json and os.WriteFile are all you need
• Look at where pipeline results are currently logged in main.go